Hitherto, Patent Document 1 proposes a thermochromic writing instrument containing a thermochromic ink, in which a friction body for thermally changing the color of the handwriting of the thermochromic ink by frictional heat is provided on a top of a cap and in which the friction body is provided at a rear end of the barrel.
Patent Document 1: Japanese Patent Unexamined Publication No. JP-A-2004-148744